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The impact of low-k dielectrics on the reliability of advanced Cu interconnects is of growing importance. As a first step to understanding this impact, we have investigated the effect of two types of polymeric low-k materials on the electromigration (EM) behavior of multilevel Al(Cu) interconnects. The two polymers used as interlevel dielectrics in this work are a fluorinated polyimide and a poly(aryl) ether. Joule heating experiments and microstructural analysis were both conducted on Al(Cu) to ensure that there were no significant microstructural or thermal differences between the polymer samples and their oxide counterparts. The resulting EM behavior can then be directly attributed to differences in the mechanical properties of the low-k and oxide interlevel dielectrics. We have observed that the low-k samples had a higher steady-state drift rate and did not reach saturation, resulting in shorter EM lifetimes. These results indicate that the short length is greatly modified with the incorporation of me...

Electromigration tests at temperatures between 340 and 400 °C and current densities between 1.0 and 3.0 MA/cm2 have been performed to determine the temperature dependence of the critical length effect in 0.5-μm-wide Cu/oxide dual-damascene interconnects with 0.1 μm silicon nitride (SiNx) passivation. A focused-ion-beam-induced contrast imaging technique is used to locate failure sites of critical length test structures. Statistical analysis [E. T. Ogawa et al., Appl. Phys. Lett. 78, 18 (2001)] yields a threshold-length product (jL)c, of 3700 A/cm, and a temperature dependence is not observed within the temperature range 340–400 °C.

Electromigration results have provided clear evidence of a short or “Blech” length effect in dual- damascene, Cu/oxide, multilinked interconnects. The test structure incorporates a repeated chain of Blech-type line elements and is amenable to failure analysis tools such as focused ion beam imaging. This large interconnect ensemble provides a statistical representation of electromigrationinduced damage in the regime where steady-state interconnect stress is manifest. Statistical analysis yields a critical length of 90 μm for interconnects with line width 0.5 μm at j=1.0×106 A/cm2 and T=325 °C.

This letter describes measurement of the biaxial modulus, coefficient of thermal expansion (CTE), and moisture uptake characteristics of hydrogen silsesquioxane (HSQ) thin films. The biaxial modulus and CTE were determined using a bending beam method, and moisture uptake was studied using a quartz crystal microbalance method. The biaxial modulus and CTE of a 0.5 μm HSQ film were measured on Si and Ge substrates and found to be 7.07 GPa and 20.5 ppm/°C, respectively. The value determined for the diffusion constant of water in a 0.7-μm-thick HSQ films is 3.61×10−10 cm2/s at room temperature.

Electromigration (EM) statistics and critical current-density line-length product (jL)/sub c/ were investigated for Cu interconnects integrated with oxide, CVD low k, porous MSQ, organic polymer dielectrics. The EM activation energy was found to be about 0.8 to 1.0 eV, which is commonly associated with mass transport at the Cu/SiN/sub x/ cap-layer interface. The lower EM lifetime and threshold product (jL)/sub c/ can be attributed to a smaller back stress due to less thermomechanical confinement in the low k structures. The confinement effect can be expressed in terms of an effective modulus B to account for EM behavior and threshold products of low k structures. For all the ILDs studied, (jL)/sub c/ showed no temperature dependence but for the organic polymer, j dependence was observed.

Electromigration (EM) characteristics were evaluated on multi-level Al(Cu) test structures with polymeric low k and standard oxide interlevel dielectrics. The two polymers used as interlevel dielectrics in this work are a fluorinated polyimide (FPI) and a poly(aryl) ether(PAE). Joule heating experiments and microstructural analysis were both conducted on Al(Cu) to insure that that there were no microstructural or other differences between the polymer samples and their oxide counterparts. The results show that the integration of polymeric low k dielectrics has a significant impact on EM performance of interconnect structures.

Electromigration (EM) lifetime characteristics and failure mechanism were investigated for Cu/porous-low-k interconnects and compared to Cu/oxide. The porous low-k dielectric was JSR LKD-5109TM, an MSQ-based spin-on organosilicate material with k = 2.2. The activation energies for EM failure were found to be 0.9 - 1.0 eV for the porous MSQ and 0.8 eV for oxide while the current density exponents for both materials were found to be similar, 1.2 - 1.3. This range of activation energies are commonly associated with mass transport at the Cu/cap-layer interface and suggest a similar mass transport mechanism; interfacial diffusion. Porous MSQ structures showed the same distinct failure morphology as observed in other Cu/low-k interconnects: voiding at the cathode and lateral Cu extrusion at the anode under the cap layer, which seems to be related to the thermo-mechanical properties of Cu/low-k interconnects. The shorter lifetime characteristics of Cu/low-k interconnects comparing to Cu/oxide can be attributed to a smaller back stress, due to less thermomechanical confinement. Results of this study indicate that thermo-mechanical properties of low-k interconnects are important parameters in controlling EM reliability of Cu/low-k interconnects.

Electromigration (EM) tests have been performed to determine early failure statistics in submicron dual-damascene Cu/oxide interconnects. Monte Carlo simulation, based on the “weakest-link” model, was developed to characterize and determine the failure modes from the cumulative distribution function (CDF) of multi-link test structures. The existence of two district failure modes (weak and strong) in our test structures was identified, where the weak mode is responsible for early failures. The weak mode is found to be void formation within the dual-damascene via, while the strong mode is associated with voiding that occurs in the dual-damascene trench. The weak mode (early failure) activation energy is found to be 1.0±0.05 eV and seems consistent with void formation that is controlled by interface diffusion between the Cu metal and its Ta diffusion barrier.

Electromigration (EM) characteristics were evaluated for multilevel copper test structures embedded in a CVD SiOC low k inter-metal dielectric. After electromigration stress testing, Cu extrusion along the interface between SiOC and the SiN dielectric diffusion barrier was revealed as the primary cause of EM failure. No evidence of cracking or mechanical weak points was observed in the bulk SiOC film; thus improved EM lifetime is expected from enhancement in the adhesion strength of SiN to SiOC. The calculated EM activation energies for 0.35 /spl mu/m via chains and 0.5 /spl mu/m via chains are 0.82 eV and 0.93 eV, respectively. The current density exponent (n) was measured to be about 1, which is consistent with the void growth mechanism in Cu. The critical length was found to decrease with increasing current density, and the j/spl middot/L/sub c/ product was determined to be approximately 7500 A/cm.

The adhesion of Al(Cu-Si) line structures on thin films of BPDA-PDA with different surface preconditioning were examined by measuring the deformation energy of the metal and interface. The properties of BPDA-PDA/Al(Cu-Si) were examined with atomic force microscopy (AFM). Although different sputtering treatments profoundly affect the adhesive properties, the sputtering does not appreciably change the topology of the BPDA-PDA. We also found evidence that even though the thickness of the interface can be very small (3–5 nm), the polymer/metal interface can greatly affect the deformation behavior of the entire system.